When using SGMII and targeting a 7-Series Transceiver interface with a Fabric Elastic Buffer, Auto-Negotiation (AN) can fail to complete.
The fabric elastic buffer does not do clock correction during Auto-Negotiation (AN) so in the case of a larger ppm clock difference between the core and link partner, the elastic buffer can overflow or underflow during AN.
The core should pause AN while the Rx elastic
buffer is reset, but in v14.2 and v14.2 (Rev. 1) AN is not correctly paused.
This issue does not affect cores generated with a 1000BASE-X, SGMII Transceiver interface without a larger fabric buffer, or a SGMII Over LVDS physical interface.
This issue only affects v14.2 and v14.2 (Rev. 1) released in Vivado 2014.2 and 2014.3.
This has been fixed in v14.3 of the core released in Vivado 2014.3.